Ad hoc networks are well known. They comprise a number of nodes corresponding to individual transmitter/receivers. For any node, there will be some nearby nodes that are in range for direct communication, and these are referred to as neighbour nodes. Other nodes will be out of range for direct communication and so may only be contacted indirectly with multiple hops via intermediate nodes. The ad hoc nature of the network means that, for any particular message, they may be many possible routes through different intermediate nodes that connect a source node with a destination node. Directing a message along a particular route requires a comparison of the routes available to select the best available. To this end, costs may be associated with any particular route based on, for example, the number of hops between nodes, the length of each hop, the speed of a node, etc. Algorithms for determining the relative costs of available routes are well known, the Dijkstra algorithm being an example.
Mobile ad hoc networks that use mobile nodes are known, and have been proposed using automobiles or aircraft as nodes (usually in combination with some fixed nodes such as base stations or ground stations). An example of an automobile ad hoc network may be found in EP-A-1,964,318. An example of an aircraft ad hoc network may be found in WO2007/059560. As the nodes are mobile and fast-moving by their very nature, the network has to be reconfigured on an ongoing basis to reflect the fact that respective pairs of nodes will move into and then out of range for direct communication with each other.
Implementing such an ad hoc network for aircraft has a particular problem in that the relative speed of aircraft may be so high. This has an adverse impact on the possible duration of a direct communication link between two nodes, particularly where the nodes correspond to a pair of aircraft flying in opposite directions. WO2007/059560 addresses this problem by modifying how costs of routes are calculated. For example, when requesting data from an unknown destination (e.g. requesting weather data for a particular area from any other aircraft having such data), potential routes for the outgoing request are weighted according to the relative speeds of successive nodes in the route, with low relative speeds being rewarded. This maximises the potential duration of a link between nodes. On the other hand, when the destination node and its position are known, WO2007/059560 proposes sending the message along a radial path, that is to say through aircraft located as closely as possible to an arc joining source and destination nodes and that are flying radially from the centre of that arc.
The present disclosure is concerned with routing messages to be sent from a source node to a selected destination node in a mobile ad hoc network. The present disclosure is also concerned with maintaining a configuration of active and inactive links to and from a source node to its neighbour nodes in a mobile ad hoc network. Ad hoc networks using aircraft are of particular concern.